If you can't take medications there's still hope for you. Vacuum Erection Therapy will help you obtain an erection firm enough for intercourse.
A good site to browse is northcoastmed.com/impotence.htm
Yes the medication could be causing erectile dysfunction. Not just the medication, but hypertension, diabetes, etc. can cause ED. The first step is to see if you can change your medication. If you have a heart condition and need to take nitrates you will not be able to take Viagra, Levitra, or Cialis.